Permanent magnet and method of making it



Patented 31, 1934 PATENT OFFICE mlllamllluder General Schenectady Electric Company, a

New York No Drawing. Ap

mortar arm nm'rnon or mamarr ,lLi uslgnor-to corporation of on June 8. 1933.

plicati Serial No. 074,216 5 Claims. (Cl. 140-21.!) 5

The present invention relates to magnetic material and more particularly to cast alloy permanent magnets and to a method of making them.

It isone of the objects of the present invention to provide a permanent magnet composed of relatively cheap materials, which may be fabricated easily and inexpensively and which has desirable magnetic qualities. In my prior copending application Serial No. 654,764, filed February 1, 1933, and entitled Permanent magnet and method of making it, I have disclosed an age hardened alloy consisting of iron, nickel and aluminum. Although the alloy described in my 'prior application has desirable magnetic properties, I have found that these properties may be further improved by the use of a relatively small quantity of cobalt in the alloy.

My improved alloy'consists'of about 6 to 15% aluminum, about 12 to %nickel'and from a fractional per cent up to about 10% cobalt, the remainder of the composition being iron. The nickel and aluminum in the alloy are preferably employed in the ratio of 2:1. Although it is not definitely known what is the solute constituent of these alloys, it is believed that it is the compound .NiAl, as nickel and aluminum in the ratio of approximately 2:1 gives the best results and this ratio is the one I prefer to employ within the ranges of composition herein disclosed.

The ingredients of the alloy. in desired proportion, are melted in any suitable 'fumace and formed into castings by pouring in a chill or sand mold. The,alloy in the as-cast condition, if it contains. about 20% or less of nickel, has fair, but not unusual permanent magnet characteristics. By normalizing the casting however, i. e. heating the casting to a temperature higher than the solution temperature of the NiAl com-, pound and then air cooling, the permanent magnet characteristics of the alloy are greatly improved. Innormalizing, the casting is heated to a temperature in the neighborhood of about 1000 C. to 1500 C. and may be cooled by quenching either in air or other suitable medium.

If the nickel content of the alloy is relatively high, for example about 22% to 30%, the alloy in the as-cast condition may have good properties. These properties may be improved by normalizing and subsequently age hardening the alloy by heating to a temperature of about 500 to 700 C. ashereinafter set forth.

The alloy in the as-cast condition, and having a 'nickel content'of about 20% or less, has a maximum energy or BHmax. of about 500,000 to 800,000. However, by normalizing the casting, the maxi- 'ture between about 500 C. to C.

' of about 600 and an age hardening period of onehalf hour provide satisfactory results. The exact length of time and the temperature of the solution-forming or normalizing treatment and of the precipitationor aging treatment although substantially as described will vary with the properties desired in the product and the use to which it is to be put. The addition of cobalt to the alloy materially aids in the control of these metallurgical changes. v

I have obtained the most satisfactory results with alloys consisting of about 12% aluminum, about 20% nickel and about 5%, cobalt the remainder of the alloy being iron. .An alloy of this composition which has been normalized and then age hardened for about one-half hour at about 600C. has a coercive force of about 460 gilberts per cm., a residual of about 800 gauss, and a maximum energy or BHmax. of about 1,650,000.

The addition of cobalt to the alloy not only improves the permanent magnet properties of the alloy but also provides a better, control of the product through heat treatment. This is of considerable value in the treatment of cast magnets of varying sectionalarea, as the cobalt apparent- 1y decreases the solubility of the nickelaluminum compound in the iron and so leads to greater dispersion on moderately rapid cooling.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An age hardened alloy magnet consisting substantially of 6% to 15% aluminum. 12% to 30% nickel, an appreciable quantity up to about 10% cobalt with the remainder iron.

2. A heat treated permanent magnet alloy consisting of about 10% to 12% aluminum, 20% to 25% nickel, an appreciable quantity up to about 10% cobalt and the remainder iron, the nickel content of the alloy being about twice the aluminum content.

3. A heat treated alloy magnet consisting of about 12% aluminum, 20% nickel, an appreciable quantity and up to cobalt and the remainder iron.

4. The method of making a permanent magnet cast alloy consisting of about 6 to alumi- 5 num, 12 to nickel, from a fractional quantity up to 10% cobalt and the reminder iron which comprises melting the ingredients of the alloy, casting the alloy and heating between about 1000 C. and 1500 C. and cooling the casting.

mg, aging the casting at a temperature below 1000" C. but high enough to cause precipitation hardness in the alloy.

WILLIAM E. RUDER.

July 31,- 1934.

Page 1, line 86, for

Leslie Frazer Acting Commissioner of Patents.

1 5. The method of making a permanent mag- CERTIFICATE on CORRECTION.

Patent No. 1,968, 569.

WILLIAM E. RUDER.

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction 'as follows: "800" read 8000; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent ffice. Signed and sealed this llth day of September, A. D. 1934- (Seal) quantity and up to cobalt and the remainder iron.

4. The method of making a permanent magnet cast alloy consisting of about 6 to alumi- 5 num, 12 to nickel, from a fractional quantity up to 10% cobalt and the reminder iron which comprises melting the ingredients of the alloy, casting the alloy and heating between about 1000 C. and 1500 C. and cooling the casting.

mg, aging the casting at a temperature below 1000" C. but high enough to cause precipitation hardness in the alloy.

WILLIAM E. RUDER.

July 31,- 1934.

Page 1, line 86, for

Leslie Frazer Acting Commissioner of Patents.

1 5. The method of making a permanent mag- CERTIFICATE on CORRECTION.

Patent No. 1,968, 569.

WILLIAM E. RUDER.

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction 'as follows: "800" read 8000; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent ffice. Signed and sealed this llth day of September, A. D. 1934- (Seal) 

